This invention related to the testing of superconducting conductors in general and move particularly to an improved method and apparatus for carrying out such testing. U.S. Pat. No. 3,976,934 teaches a method for the continuous, contactless testing of an elongated conductor which consists at least partially of superconductive material. The conductor, with the superconductive material which is in the superconducting state, is moved through an external magnetic field which induces shielding currents in the superconductive material. The magnetic field generated by these shielding currents is measured. The corresponding apparatus for implementing this method contains a cryostat in which a cylindrical superconducting magnet coils for generating the external magnetic field is arranged. Further, means are provided in the cryostat for introducing the conductor into the magnetic field of the superconductor magnet coil approximately parallel to the axis of the coil, for deflecting the conductor at right angles to the coil axis and, thereby, to the external magnetic field, and for bringing the conductor out again approximately parallel to the coil axis, as well as at least one magnetic field probe arranged in the vicinity of the deflection point.
The known method and the corresponding apparatus are based on the measurement principle of pulling the conductor, in the superconducting state, through a magnetic field, such that superconducting shielding currents are induced, and then measuring the field of these currents. Since disturbances in the superconductor affect its shielding currents and thereby, their own fields outside the superconductive material, the field changes connected therewith can be measured by means of magnetic field measuring probes and be correlated with the corresponding points of the conductor.
The known method and the corresponding apparatus are particularly well suited for ribbon shaped superconductors. If, however, elongated conductors having a superconducting layer which extends to a large degree in three dimensions, e.g., a cylindrically shaped layer, are to be tested for freedom from defects with this known method and apparatus, then there may be surface areas in which defects are not registered reliably.